diff --git a/tools/build.sh b/tools/build.sh
index e9bb81a..5b029d6 100755
--- a/tools/build.sh
+++ b/tools/build.sh
@@ -11,7 +11,7 @@ die() {
 }
 
 die_usage() {
-	die "usage: $0 example-1.2.3-0 [--purge]"
+	die "usage: $0 example-1.2.3-0 [--purge] [--bind directory]"
 }
 
 ere_quote() {
@@ -23,9 +23,10 @@ log_cmd() {
 	"$@"
 }
 
-eval set -- $(getopt --options "" --longoptions purge -- "$@")
+eval set -- $(getopt --options "" --longoptions purge,bind: -- "$@")
 while true; do
 	case "$1" in
+		--bind)  opt_bind=1;bind_dir=$2;shift 2;;
 		--purge) opt_purge=1;shift;;
 		--) shift;break;;
 		*) die "internal error: unknown option $!"
@@ -57,10 +58,27 @@ if [ -n "$opt_purge" ]; then
 	test -z "$PKG" && die "internal error: PKG is empty"
 	log_cmd find "/pkg/$PKG" -mindepth 1 -delete
 	test "$(stat -c %U "/pkg/$PKG")" = "build" || log_cmd chown build:build "/pkg/$PKG"
+	if [ -n "$opt_bind" -a -d "$bind_dir/pkg_bindmnt" ]; then
+		log_cmd find "$bind_dir/pkg_bindmnt" -mindepth 1 -delete
+	fi
 fi
 
 chmod a+rx "$PKG.build.sh"
 
+if [ -n "$opt_bind" ]; then
+	mkdir -p "$bind_dir/pkg_bindmnt"
+	chown build:build "$bind_dir/pkg_bindmnt"
+	# check that '/pkg/$PKG' differs from intended location (i.e. isn't mounted already)
+	if [ $(stat --format=%D:%i "$bind_dir/pkg_bindmnt") != $(stat --format=%D:%i /pkg/$PKG) ]; then
+		log_cmd mount --bind "$bind_dir/pkg_bindmnt" /pkg/$PKG
+		# prevent automount from unmounting
+		exec 3</pkg/$PKG/.
+		test $(stat --format=%D:%i "$bind_dir/pkg_bindmnt") = $(stat --format=%D:%i /pkg/$PKG) || die "unable to mount and lock '$bind_dir/pkg_bindmnt' on /pkg/$PKG"
+	else
+		die "'$bind_dir/pkg_bindmnt' is already mounted on /pkg/$PKG (try 'umount /pkg/$PKG')"
+	fi
+fi
+
 echo "sudo -u build script -q -e -c \"./$PKG.build.sh\" /package/pkg/$PKG/$PKG.build.log"
 (
 	sudo -u build script -q -e -c "./$PKG.build.sh" /package/pkg/$PKG/$PKG.build.log
@@ -70,3 +88,14 @@ echo "sudo -u build script -q -e -c \"./$PKG.build.sh\" /package/pkg/$PKG/$PKG.b
 # make double sure PKG is not empty even if bugs are introduced in code above
 test -z "$PKG" && die "internal error: PKG is empty"
 log_cmd chown -R bin:bin "/pkg/$PKG"
+
+if [ -n "$opt_bind" ]; then
+	test -z "$PKG" && die "internal error: PKG variable is empty"
+	test $(ls "/pkg/$PKG" | wc -l) = 0 && die "/pkg/$PKG contains no files"
+	# withdraw our 'foot in the door'
+	exec 3<&-
+	log_cmd umount /pkg/$PKG
+	# enforce single filesystem as source, and ignore .*
+	log_cmd cp -ax $bind_dir/pkg_bindmnt/* /package/pkg/$PKG
+	log_cmd chown bin:bin "/package/pkg/$PKG"
+fi